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Title

COMPUTATION OF THIN AIRFOIL AERODYNAMICS FOR MICRO AIR VEHICLE APPLICATIONS

Creator

Baez Guada, Alejandro

Date

2013-04-29, 2013-05

Description

With the significant interest in the development of micro air vehicles with gust resistant capabilities, active flow control has become a main...
Show moreWith the significant interest in the development of micro air vehicles with gust resistant capabilities, active flow control has become a main challenge in enhancing flight conditions. The current flow control techniques are limited at suppressing fluctuations in the lift induced by unsteady freestreams and while undergoing fast maneuvers. As a result of the time delay associated with the actuation input and formation of the leading edge vortex, closed-loop controllers are limited by the bandwidth to suppress fluctuation in the lift under unsteady freestreams. Therefore, the recognition of the direct interaction of the controller with the formation of vortex shedding suggests the development of new techniques for flow control. For the sinusoidal oscillating freestream, the knowledge of the time scales in response to actuation and the phase between the unsteady freestream and lift time series are useful in the implementation of the feed forward controllers suppressing lift fluctuations. Moreover, prospective solutions have been conceptualized in the implementation of the leading edge separation sensor and the gust load alleviation controller that would allow the instantaneous response to enhance lift under unsteady freestreams conditions. With the increasing computational power and reliance on turbulence models, the numerical simulations facilitate the investigation of thin airfoil aerodynamics at post-stall angles of attack under steady and unsteady freestreams. The computations of turbulent flows for external flow aerodynamics are challenging as a result of the presence of separated flow. The detachment of boundary layers is by nature three-dimensional and time dependent. Therefore, simulating these flows is problematic and requires high computational cost. Thin shear layers are common in external aerodynamic flows demanding very fine near-wall discretization to solve for separation points. The growth of the boundary layer, separation, and mixing length scales require complex approaches for accurate results. xviii In the present study, the performance of the turbulence models is investigated in numerical predictions of thin airfoil aerodynamics at post-stall angles of attack. The results suggest that low computational cost turbulence models fail at treating separated flows. Moreover, the instantaneous locations of separation and stagnation points in response to the changes in the lift for steady and unsteady flows were investigated. The amplitude and frequency of the time series of the separation and stagnation point location are highly correlated with the characteristics of the lift oscillations. Therefore, the recognition of separation or stagnation point locations at the leading edge of the wing could provide the direct information of the gains and drops in the lift for active flow control applications.
M.S. in Aerospace and Mechanical Engineering, May 2013
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